WD external hard drive

I need help, i have a western digital external hard drive that works completely fine on my PC, i can see the data and write to it and everything but with my Imac it doesnt even appear anywhere, not even in disk utility?
pleaaase help

Is the drive formatted to NTFS? And.. what kind of an iMac do you own? Intel? PowerPC?

Regards.

I'm pretty sure the drive is formatted to NTFS, because it only works on my dell computer with windows xp, and i think it's Intel.

Well there is your problem. Mac can't read NTFS format without special drivers. Even then they aren't exactly that reliable.